A polyester resin has been widely used in industry for fibers and films since the polyester resin has excellent heat resistance, chemical resistance, mechanical properties, and electrical properties, and excellent cost/performance. In recent years, a biodegradable aliphatic polyester in the natural environment has been vigorously researched from the viewpoints of protection of the natural environment. In particular, a poly(lactic acid) resin is expected, for example, for packing materials such as a container and a film, fiber materials such as clothes, a floor mat, and an interior material for vehicles, and molding materials such as a housing and a part of electrical and electronic products since the poly(lactic acid) resin has a melting point as high as 160 to 180° C. and excellent transparency.
However, the polyester resin including the polylactic acid) resin has a disadvantage in which a molded product produced by injection molding or the like particularly without drawing is likely to have lower crystallinity and be softened at a temperature exceeding a glass transition temperature of about 60° C. This is because the polyester resin generally has an extremely low crystallization rate although it is a crystalline resin. In order to increase the crystallinity, a method of increasing the temperature of a mold during injection molding to extend the cooling time in the mold has been attempted. However, the method has a problem of productivity since a molding cycle is extended. In order to produce a polyester resin molded product with high productivity and use the molded product for a wide variety of applications, an increase in the crystallization rate and the crystallinity and an improvement in molding processability and heat resistance have been attempted.
As a method of improving the crystallization rate of a polyester resin, a method of adding a crystal nucleating agent has been generally known. The crystal nucleating agent acts as a primary crystal nucleator of a crystalline polymer to promote crystal growth, and serves to make the crystallite size fine and increase the crystallization rate. As a crystal nucleating agent of a polyester resin, metal salts of organic acids such as potassium benzoate and magnesium stearate and inorganic compounds such as talc, silica, and calcium sulfate have been conventionally proposed. As a crystal nucleating agent of a polylactic acid) resin, inorganic particles including talc or boron nitride that has a particle diameter equal to or less than a specific particle diameter (Patent Document 1), an amide compound of a specific formula (Patent Documents 2 and 3), a sorbitol derivative of a specific formula (Patent Document 4), a phosphoric acid ester metal salt of a specific formula (Patent Document 5), and the like have been disclosed. It has been disclosed that a metal salt of specific phosphonic acid compound, specifically zinc phenylphosphonate exhibits excellent performance (Patent Document 6).